The assignee of the present invention manufactures and deploys spacecraft for, commercial, defense and scientific missions. Many such spacecraft operate in a geosynchronous orbit having a period equal to one sidereal day (approximately 23.93 hours).
Such spacecraft are equipped with on board propulsion systems, including chemical and/or electric thrusters, for orbit raising from a launch vehicle transfer orbit (or “parking orbit”) to an operational orbit, for example, to a geosynchronous orbit; for stationkeeping once disposed in the operational orbit; and for attitude control/momentum management purposes.
In general, the known techniques provide that individual thrusters are relatively “specialized” with respect to the mission functions each thruster performs. For example, propulsion subsystems have been configured whereby electric thrusters perform north south stationkeeping and momentum management, but not orbit raising. As a further example, some propulsion subsystems have been configured whereby electric thrusters perform some orbit raising and/or north south stationkeeping, but separate chemical thrusters perform east-west stationkeeping and some orbit raising. Such a system is disclosed in U.S. Pat. No. 6,032,904, issued to Hosick (hereinafter, “Hosick”) and assigned to the assignee of the present invention, the disclosure of which is hereby incorporated in its entirety into the present disclosure for all purposes. Additional station-keeping and momentum management techniques are described in U.S. Pat. Nos. 4,767,084, 6,296,207, and U.S. Pat. Pub. 2014-0138491, assigned to the assignee of the present invention, the disclosures of which are incorporated by reference into the present application for all purposes.
Improved techniques are desirable to enable meeting the full gamut of propulsion missions with a reduced equipment manifest while providing adequate redundancy/high reliability.